The present invention relates to a method of making multi-wall metal tube and to the resultant tube. More particularly it relates to multi-wall metal tubing produced in a continuous process from precut metal strip.
U.S. Pat. No. 1,431,368 to Bundy, entitled "Tubing", discloses a multi-wall metal tube formed of metal strip that has been tinned or painted with solder and then longitudinally wrapped around a stationary mandrel to form a multi-wall tube. In the process disclosed, the mandrel is used to support the tube at its inside diameter at a finishing stand. This mandrel assures a tight tube construction and size tolerance control. While the process of the Bundy patent has represented the industry standard for over forty year, an opportunity for improvement has been noted with a resultant tube that is considered at least equal to that currently used. Specifically, the mandrel at the finishing station is a source of continuous concern, and its maintenance a substantial cost factor.
The present invention represents an improvement of the prior art process by elimination of the mandrel. The finished multi-layer tube is also considered new to the art.